1. Field of the Invention
The present invention relates to an apparatus and method for bend-shaping a glass sheet into a bi-directionally curved shape.
2. Description of the Prior Art
Many glass sheets for use as automobile side windows are bent in only one direction (hereinafter referred to as “single-curved glass sheet”). Such glass sheets are known from, for example, Japanese Patent Publication No. SHO-43-11768 entitled “METHOD OF TRANSFERRRING HEAT BETWEEN A GLASS SHEET AND GASES FLOWING IN CONTACT WITH THE SHEET” (corresponding to U.S. Pat. No. 3,332,759 and No. 3,332,760).
For design reasons, such side window glass sheets are often required to be bent in two directions, namely, a first direction and a second direction normal to the first direction (hereinafter referred to as “dual-curved glass sheet” and often as “complexly-curved glass sheet”). An apparatus for bend-shaping such a complexly-curved glass sheet is proposed in, for example, Japanese Patent Laid-Open Publication No. HEI-5-009037 “METHOD AND APPARATUS FOR BEND-SHAPING A GLASS SHEET” (corresponding to U.S. Pat. No. 6,014,873). An overall arrangement of the proposed apparatus is schematically illustrated in FIG. 15 hereof.
As shown in FIG. 15, the proposed apparatus includes a heating furnace 150 having an array of beds 151 (only one shown) positioned therein. Air is jetted from upper surfaces 151a of the beds 151 to floatingly support a glass sheet 153 for successively transferring, via a transfer means not shown, the glass sheet 153 over the upper surfaces 151a of the beds 151 in an arrowed direction.
Toward an outlet 150a of the heating furnace 150, the upper surfaces 151a of the beds 151 gradually become curved in a transverse direction (normal to a direction of transfer of the glass sheet 153) so that they have an upwardly convex shape. Thus, as the glass sheet 153 is transferred over the upper surfaces 151a in the arrowed direction, the glass sheet is gradually bent by its own weight (self-sagging) into a shape complementary with the shape of the beds 151 to thereby provide a single-curved glass sheet.
After arrival at a position proximate to the outlet 150a of the heating furnace 150, the single-curved glass sheet 153 advances inclinedly upwardly over beds 155, 156 disposed within the heating furnace (hereinafter called “in-furnace beds”) in an upwardly inclined fashion. These beds 155, 156 have respective upper surfaces 155a, 156a curved not only in a transverse direction but also in the direction of transfer of the glass sheet. Thus, transfer of the single-curved glass sheet 153 over those beds 155, 156 causes the glass sheet 153 to become a complexly-curved glass sheet which is bent in both transverse and transfer directions of the glass sheet 153.
Continuously, the complexly-curved glass sheet 153 is transferred to a cooling bed 160 positioned proximately to and externally of the outlet 150a of the heating furnace 150 (hereinafter called “out-furnace bed”), where, while being supported by air jetted from an upper surface 160a of the out-furnace bed 160 in a floated fashion, the complexly-curved glass sheet 153 is cooled by cooling air jetted from cooling means 162 positioned upwardly of the glass sheet 153.
Reference is made next to FIG. 16 illustrating a conventional in-furnace bed on an enlarged scale.
Upper surface 156a of the in-furnace bed 156 is curved both in a direction of its width W and in a direction of its length L. The upper surface 156a of the in-furnace bed 156 has a multiplicity of air jet holes 157. Air is jetted from the air jet holes 157 to floatingly support the single-curved glass sheet 153 over the upper surface 156a, whereupon the glass sheet 153 is bent also in the direction of transfer of the glass sheet to thereby provide the desired dual-curved glass sheet.
Similarly to the upper surface 156a of the in-furnace bed 156, the upper surface 160a of the out-furnace bed 160 shown in FIG. 15 is curved both in a transverse direction and in a direction of transfer of the glass sheet.
Apart from the publication just described, an apparatus for bend-shaping a glass sheet into a dual-curved shape is also disclosed in Japanese Patent Laid-Open Publication No. HEI-6-191867 (U.S. Pat. No. 5,522,912). In the apparatus of this publication, a final bed disposed in heating furnace is curved in a transverse direction but is linear in a direction of transfer of a glass sheet. The final bed has an upper surface of uphill shape, that is, uprising toward an outlet of the heating furnace. In contrast, a quenching bed disposed externally of the heating furnace has an upper surface of downhill shape. Upon transfer from the final bed onto the quenching bed, the glass sheet is formed into a dual-curved glass sheet.
Another method and apparatus for bend-shaping a glass sheet is disclosed in Japanese Patent Laid-Open Publication No. HEI-9-202633. This publication teaches jetting hot air downwardly and combining a downward force produced by the jetted hot air with the weight of a glass sheet being bent to thereby facilitate bending of the glass sheet. As a result, the time required for bending a glass sheet can be shortened. Further, the hot air is jetted downwardly through a gap between an inclined bed and a cooling bed to provide an air curtain which keeps cooling air away from the glass sheet to thereby maintain the glass sheet at its softening temperature.
It is costly to install two lines of manufacture, namely, one for manufacturing the single-curved glass sheet, as described above, and the other for manufacturing the dual-curved glass sheet, as also described above. If a single line of manufacture is made available for use in producing both the single-curved glass sheet and dual-curved glass sheet, this will achieve substantial cost reduction.
For example, the in-furnace beds 155, 156 of the bend-shaping apparatus disclosed in Japanese Patent Laid-Open Publication No. HEI-5-009037, discussed with reference to FIG. 15, may be replaced with new beds 151, 151 curved only in a transverse direction, while the out-furnace bed 160 may be replaced with a bed curved only in a transverse direction. This makes the bend-shaping apparatus available for use in manufacturing a single-curved glass sheet.
Thus, only the bend-shaping apparatus as shown in FIG. 15 may be installed for manufacturing a single-curved glass sheet. When desired, relevant parts of the apparatus may be substituted by other parts to manufacture a dual-curved glass sheet. However, this involves tedious operations to switch the apparatus from one mode of operation to another by replacing the beds for manufacturing a single-curved glass sheet with the beds 155, 156 for manufacturing a dual-curved glass sheet.
Further, upon changing the beds for manufacturing the single-curved glass sheet to the beds 155, 156 for manufacturing the dual-curved glass sheet, it is necessary to lower the temperature of the heating furnace from about 700° C. (glass softening temperature) to an atmospheric temperature. In addition, after the beds for manufacturing the single-curved glass sheet to the beds 155, 156 for manufacturing the dual-curved glass sheet, the temperature within the furnace 150 must be risen to about 700° C. again. Consequently, bed changing takes a relatively long time, thereby deteriorating productivity. Moreover, it is necessary to provide two different types of beds, namely, beds 155, 156, 160 for manufacturing the dual-curved glass sheet and beds for bending the glass sheet, thereby increasing the cost of glass sheet production.